Like water flowing through proper plumbing, your audio signals need good cables and connections to carry them from place to place.
Imagine the mayhem you’d have in your home if all your plumbing was installed wrong–really wrong. Your kitchen disposal feeds the bathtub faucet, the bathroom sink drains into the washroom hot-water tap and the toilet–well, you don’t really want to know what the toilet’s connected to.
If you picture your audio signal as water and your audio cabling as the pipes that carry it, you’ll have a better grasp on the importance of wiring your audio lines correctly. Connecting audio cables wrong will give you the electronic equivalent of a glass of murky, brown water–your audio signals will carry all kinds of unsavory pollutants.
Before you can connect your equipment properly, you need to understand the various cables and connectors you’ll encounter as you make and edit video. These come in various shapes, sizes and styles. Figure 1 shows you what they look like.
You’ll usually have audio on one of four standard connectors: RCA, XLR, minijack or 1/4-inch. Each of these connectors can carry signals of various types in addition to audio, but that’s the topic of another article.
The RCA jack is probably the most common audio connector in the consumer realm. It can carry video or audio, and is cheap to manufacture. It’s not the sturdiest jack, though, and it’s easy to disconnect accidentally. RCA audio cables usually come in pairs (often black and red in color) for carrying stereo audio. Using black for left and red for right is the easiest way to remember which is which, since both “red” and “right” start with “R.”
The XLR jack is most commonly used for connecting microphones to mixers or recorders. The XLR mike jack carries a special balanced signal designed to reject noise. (Microphone signals are tiny and vulnerable, and need all the help they can get.) XLR jacks lock into place, making them much sturdier than RCA or 1/4-inch jacks. In most professional applications, XLR jacks carry all the audio–not just mike signals.
You’ll find minijack connectors on microphone products designed for direct connection to the camcorder. Accessory microphones often use a minijack, as do many wireless microphone receivers. The minijack connector can be stereo or mono.
Though you may run across it occasionally, the 1/4-inch or “phone plug” connector is not as common in video production as it is in audio recording. Quarter-inch connectors usually carry audio from instruments, such as guitars and/or keyboards. They may also carry speaker-level signals on unshielded wire. Important note: never plug a speaker output into an audio input. You may fry your gear.
If you find yourself dealing with 1/4-inch phone plugs in your audio setup, don’t fret: it’s a simple matter to use an RCA-style adapter on a 1/4-inch signal cable. This configuration will work fine for most video applications.
What’s the Connection?
Connecting audio lines is usually very straightforward. Outputs always go to inputs, and inputs to outputs. Wiring an output to an output won’t harm your equipment, but it’s a bit like trying to move a piano by pushing on both sides. Nothing happens. The same goes for wiring inputs to inputs.
As the complexity of your video system increases, making the proper connections gets harder. It’s advisable, if you have a hard time picturing the signal flow in your head, to scratch out a rough diagram on paper. (See figure 2 for an example.) Keep this handy for when you need to remove, replace or bypass a piece of equipment.
If you’ve got your gear cramped into a small space without rear access, changing even one piece of equipment can be a real nightmare. The best solution is to use drafting tape or artist’s tape to label each connector. Simply fold a 1.5-inch piece of tape all the way around the cable near the connector, and write the cable’s destination on the tape. Drafting or artist’s tape won’t leave residue or harden like standard masking tape. When it comes time to change your setup, the tape labels save you having to trace out every cable. (I recently had to remove and replace an audio mixer with nearly 50 connectors attached. Thanks to tape labels, the swap took less than five minutes.)
Stereo and Mono
Unless you’re producing videos with full surround-sound audio, you’ll be dealing with just two signal types: stereo and mono. Mono is the simpler of the two, consisting of a single audio signal carried on one cable. Even if it’s coming out of multiple speakers, mono audio seems to come from just one point in front of the listener.
Stereo audio uses two signals, two wires, two amplifiers and two speakers to place sounds across a “soundstage.” Sounds can then seem to emanate from either speaker, or anywhere between the two. Almost like the difference between binoculars and a telescope, stereo audio gives sound “width.” You’ll find most stereo signals on a pair of RCA cables. Stereo camcorder microphones will often use a stereo minijack, much like that found on portable stereo headphones.
Connecting like equipment (stereo or mono) together is a piece of cake. But what about when you need to convert from one to the other? No problem, provided you remember a few simple guidelines. Let’s start with a look into attaching a stereo source to a mono input.
If you have a stereo camcorder and a mono VCR or editing system, you’ve probably faced this situation before. First off, resist the instinct to combine the left and right stereo outputs with a splitter. Splitters, or “Y” cables, are for making two sources out of one, and not the other way around. When you patch the left and right outputs of your equipment through a Y cable, you’re wiring these two circuits directly together. While this may not seem to pose any problems, it can cause harm to certain pieces of gear.
Your best bet is to use just one of the stereo outputs, leaving the other unused. Which one should you use? Convention dictates using the left, but there are times this isn’t the best choice. Say you shot a lecture or concert from near the right side of the stage. Your stereo camcorder’s right mike picked up clean audio from the loudspeaker located to your right. The left mike picked up more audience noise and room ambiance. If clarity and audibility are your goal, use the right signal.
It is possible to combine the left and right signals into a mono signal, but you should always try to do this with an audio mixer. This will electrically “buffer” the left and right outputs so they’re not feeding directly into each other.
Recording a mono signal on a stereo VCR or camcorder presents less of a challenge. With a Y cable, you can record the same mono signal on both left and right tracks. On playback, the end result will be mono sound that seems to be coming from directly between the two speakers. You can also record the mono signal onto just one of the two stereo inputs (usually the left).
By now, you should have a better idea how to connect your audio and video equipment for best results. Here are a few parting tips to help ensure your connections continue to pass pristine, unpolluted audio:
- When disconnecting a cable, always pull by the connector itself. Pulling directly on the cable to detach it will eventually ruin the cable, guaranteed.
- If you have to convert from one connector type to another, use as few adapters as possible. Each adapter you add increases the odds of a flaky connection. If you’re handy with a soldering iron, make a custom cable to replace your most-frequently used adapters.
- Don’t bother with fancy, hi-fidelity cables bearing gold connectors and designer price tags. They may offer a minuscule improvement, but only on a test scope. The real-world performance of these cables rarely justifies the added cost. At the same time,
- Avoid flimsy, thin cables that look like they’ll break the first chance they get. Stick with good-quality, sturdy-looking cables. Audio cables the size of angel-hair pasta don’t hold up to repeated use.
- If you’re trying to interface with an existing sound system while on a shoot, don’t assume you know what a cable is carrying just because you recognize the connector. Though we have some established guidelines for connector usage, no real rules apply. Try to trace any cable you plan to use back to its source. Make sure the signal type and strength are correct before you plug it into your equipment. (For a more complete discussion on cables, connectors and signal types, see “Cables and Connectors: Handle with Care” in the September, 1996 issue of Videomaker.)
So when it comes to audio connections for video, you don’t have call a plumber. Just follow the directions listed above and your signals should flow smoothly from source to destination.